Drug delivery devices may have application where regular injection by persons without formal medical training is necessary. This is increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease. In practice, such a drug delivery device allows a user to individually select and dispense a number of user-variable doses of a medicament.
There are basically two types of drug delivery devices: resettable devices (i.e., reusable) and non-resettable (i.e., disposable). For example, disposable pen delivery devices are supplied as self-contained devices. Such self-contained devices do not have removable pre-filled cartridges. Rather, the pre-filled cartridges may not be removed and replaced from these devices without destroying the device itself. Consequently, such disposable devices need not have a resettable dose setting mechanism. Some embodiments are applicable for both types of devices, i.e. for disposable devices as well as for reusable devices.
A pen-type drug delivery device, or pen delivery device, is a common type of a drug delivery device for liquid drug delivery. Pen delivery devices (so named because they often resemble an enlarged fountain pen) generally comprise three primary elements: a cartridge section that includes a cartridge often contained within a housing or holder; a needle assembly connected to one end of the cartridge section; and a dosing and delivery section connected to the other end of the cartridge section. A cartridge (often referred to as an ampoule) typically includes a reservoir that is filled with a medication (e.g., insulin), a movable rubber type bung or stopper located at one end of the cartridge reservoir, and a top having a pierceable rubber seal located at the other end.
The needle assembly may typically be a replaceable double-ended needle assembly. Before an injection, a replaceable double-ended needle assembly is attached to one end of the cartridge assembly, a dose is set, and then the set dose is administered. Such removable needle assemblies may be threaded onto, or pushed (i.e., snapped) onto the pierceable seal end of the cartridge assembly.
A further differentiation of drug delivery device types refers to the drive mechanism: There are devices which are manually driven, e.g. by a user applying a force to an injection button, devices which are driven by a spring or the like and devices which combine these two concepts, i.e. spring-assisted devices which still require a user to exert an injection force. The spring-type devices involve springs which are preloaded and springs which are loaded by the user during dose selecting. Some stored-energy devices use a combination of spring preload and additional energy provided by the user, for example during dose setting. Some embodiments are applicable for both types of drive mechanisms.
The dosing section or dose setting mechanism is typically the portion of the pen device that is used to set a dose. Alternative terms are selecting or dialing a dose. During an injection, a spindle or piston rod contained within the dose setting mechanism presses against the bung or stopper of the cartridge. This force causes the medication contained within the cartridge to be injected through an attached needle assembly. After an injection, the needle assembly is usually removed and discarded.
The dose setting mechanism usually includes a component that moves during dose setting in dependence on the desired dose in one direction; then, during dose delivery, it return to its initial position. The dose may be selected and set between a zero dose, 0 U, and a maximum dose. An advantage of some embodiments may be that the dose setting mechanism is suitable for setting a minimum dose size, which is larger than zero, ensuring that the user cannot dispense less medicament than required.